1. Field of the Invention
This invention concerns solid state displacement elements comprised principally of inorganic layered compounds and in which a strain is produced when a voltage is applied.
2. Description of the Related Art
Electrostrictive type actuators constructed from solid state displacement elements in which a strain is produced when a voltage is applied, for example, for driving damping force control valves for vehicles and fuel injection valves or fuel control valves for the fuel injection devices of internal combustion engines etc.
However, the electrostrictive elements that have been used in the past have generally been formed with ceramics in which lead zirconate titanate (PZT) forms the principal component. These are manufactured using the methods of powder metallurgy. That is to say, raw materials comprising of 61.3 wt. % of PbO, 10.7 wt. % of TiO.sub.2 and 21.1 wt. % of ZrO.sub.2 as the principal components are weighed out and mixed by wet ball-milling. The mixture is then pre-baked for 3-10 hours at 700.degree.-900.degree. C. and then ball-milled again and dried. A binder such as poly (vinyl alcohol) is then added and, after pressure molding at a pressure of 300-1000 kg/cm.sup.2, the material is baked for 1-3 hours at 1200.degree.-1300.degree. C.; the external shape is ground and an element is obtained.
However, the electrostrictive elements used in applications such as those aforementioned generally require a large amount of displacement. With the conventional electrostrictive elements the extent of the displacement is not sufficient and so it is necessary to apply an excessive voltage to the said electrostrictive elements to increase the amount of the displacement, but when such an excessive voltage is applied the insulation properties of the said element are reduced and, moreover, there is a further disadvantage in that shorting is liable to occur between a pair of adjacent electrodes.
The aim of this present invention is to eliminate such disadvantages of the conventional technology and provide novel solid state displacement elements with which the extent of displacement can be obtained by the application of a voltage.